This invention relates generally to control systems for combustors in gas turbine engines having air bypass systems and in particular to a control system that arrests flashback in such combustors.
Lenertz et al. U.S. Pat. No. 6,070,406 entitled xe2x80x9cCombustor Dilution Bypass Systemxe2x80x9d discloses a combustor having two combustion systems generally denoted by the letters A and B as shown in FIG. 1. Each of these systems includes an air bypass system having a valve 12 with an inlet port 16, and two exit ports 18 and 20. Inlet port 16 is connected to an inlet duct 17 for receiving compressed air from the combustor plenum 19 that circumscribes the combustion chamber 60 which is defined by a combustor wall 62. Exit port 18 connects to the premixer duct 22 which leads to the premixer injector 64 that injects tangentially a mixture of fuel and air into the combustion chamber 60. The injector 64 has a fuel nozzle 66, a venturi 70, a premix chamber 68 and an igniter 72. In operation, the fuel nozzle injects a fuel-air mixture into the premix chamber 68. In the premix chamber additional air is added through premixer duct 22. The igniter 72 ignites this mixture during engine starting creating a hot gas 74 that flows into and around the combustion chamber 60. The second exit port 20 connects to the bypass duct 24. The valve 12 includes a rotatable valve rotor 26 for selectively controlling the relative proportions of airflow to premixer duct 22 and bypass duct 24. The position of the rotor 26 is controlled by an electronic unit for the gas turbine engine in which these combustion systems are deployed.
Flashback involves the flame from the combustion chamber 60 being drawn back into the venturi 70 and premix chamber 68 and may be caused by a backflow from the combustion chamber due to compressor instability, transient flows, varying operating conditions and/or varying fuel properties. Because the metals or alloys used to form the venturi and premix chamber cannot withstand high temperatures for significant amount of time, damage can quickly occur to these structures in the presence of a flashback. The flashback can be arrested by increasing the airflow into the venturi and premix chamber.
Accordingly, there is a need for a control and method for increasing air flow to the injector 64 in the event of a flashback.
An object of the present invention is to provide for a control and method for arresting flashback in a gas turbine engine combustion system having a venturi for delivering a mixture of air and fuel to a combustion chamber and a valve for controlling the amount of air flowing to the venturi.
The present invention achieves this object by providing a flashback control system and method having a flashback detection routine, a valve position trim routine, and a reference flame temperature adjustment routine. The flashback detection routine detects a flashback in the venturi by comparing the temperature at the venturi to the temperature of the air entering the valve. The valve position trim routine receives this flashback signal and in response causes the valve to open until the flashback is arrested. Finally, to prevent the flashback from recurring, the reference flame temperature adjustment routine adjusts a reference flame temperature in the control system so as to prevent the valve from returning to the position at which the flashback occurred.
These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.